The Galaxy grabbed the lead when Keane dribbled down the left side, worked his way to the edge of penalty area and sent a left-footed chip into the box, where Sarvas headed it into the net.
Hector Jimenez added an insurance tally in the 80th minute off assists from Keane and Robbie Rodgers as Los Angeles (9-7-3) surged to within a point of second-place Dallas in the Western Conference standings.
Dallas (8-4-7) fell to the Galaxy for the fifth time six meetings dating back to 2011.
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